As a result of recent advancement in researches on the mechanism of skin deterioration, it has been confirmed that, macroscopically speaking, the feeling of skin dryness and the roughening of the skin are not only caused by the decline of metabolism due to aging but also intricately involved with the effect of factors such as sunlight (ultraviolet), drying, and oxidation. It has been revealed that collagen fibers, which are the most primal matrix components of the dermis, are significantly reduced by the effect of these factors. Wrinkles and sagging of the skin are increased if the machinery for retaining the tension of the skin, such as resilience and elasticity, supported by the collagen fibers is destroyed due to the effect of the factors such as ultraviolet. Since collagen can hold water in molecules thereof and thereby helps to keep the skin moisturized, if collagen is destroyed by an external factor, the skin is dried and roughened. From the above, a skin collagen production-promoting agent is desired that can prevent wrinkles and sagging of the skin by promoting the biosynthesis of collagen, which is one of the major components of the dermic layer, without safety problems.
Transforming growth factor beta (TGF-β) is one of the growth factors present in the milk of mammals. The TGF-β family includes five subtypes, which are proteins forming a dimer of about 25 kDa by disulfide bonds. The TGF-β family has a function of regulating the promotion/inhibition of cell proliferation, biosynthesis, differentiation, and apoptosis. The effect of inducing differentiation in animal cells has been confirmed as a useful effect of TGF-β (Patent Document 1). TGF-β is also reported as a growth factor of fibroblast cells in the skin (Non-Patent Literature 1).